[jsheard]

Partly because they're a niche product and making legended keycaps is more expensive, and partially because ergo layouts are so varied that it's hard to accommodate everyone. Especially if the keycap profile has different shapes for each row so they're not entirely interchangeable.

There are a few low-profile legended keycap sets around but they typically only cover the "top" layer, which is the easiest to remember anyway. If you want legends which show every function of every key you'd have to get them custom laser etched to match your personal keymap.